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Dual Subs

Discussion in 'Subwoofers' started by eviljohn2, Jan 22, 2005.

  1. eviljohn2

    eviljohn2
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    Some of you probably know that I use a BK XLS200 for subwoofer duties, the merits of which are discussed elsewhere so please don't ask about it here!

    I'm seriously considering throwing caution to the wind and getting another XLS200 to make a pair in my room. Having read the Harman white paper on multiple subs I'm reasonably clued up on location benefits and in the future I'll consider placing them in different parts of the room, but for now, in a room that fulfils duties as my office/bedroom/living room I don't really have space for double the footprint which leads me onto stacking a pair.

    Does anyone hiding in the woodwork around here have any experience of this? I've read a fair amount about it on the AV123 forums and am reasonably confident I can calibrate them to good effect (parametric equalisers and physics degrees do have benefits it would seem!).

    More importantly, can anyone recommend something I can put between them without damaging the finish (ie. nothing sticky like blu-tac)? I currently use doorstops as feet for my XLS200 and could get a few more of these to put between them but there are loads of other options around such as Auralex Mopads or even just a towel.

    At the moment I'm inclined to go with doorstops again as they're cheap and work pretty well. :)
     
  2. Nimby

    Nimby
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    I've used a pair of large subs in very large rooms to acoustically support Linn Kans for stereo. Co-location (with the speakers) was important due to the high 120Hz (-3dB) natural roll off point. :blush:

    HTF 'Speakers' has some discussion on stacking SVS PB10-ISDs to achieve a world-class performance. You might try four XLS200s! :devil:

    As to seperating the little buggers I would recommend closed-cell foam camping matresses as sandwich fillers. :)

    Nimby
     
  3. eviljohn2

    eviljohn2
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    Thanks Nimby, should have guessed you'd have tried this craziness already! I think I'll just use mine for the LFE channel so the only localisation problem is likely to be that they're quite so visible, although will still be a little smaller than the larger SVS cylinders. 2 forwards firers will look pretty mean I hope :devil:

    Have you got a link to those nutters stacking PB10's? :eek:

    Camping mat is a great idea that has moved to the top of the list for now. :thumbsup:
     
  4. Nimby

    Nimby
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    Just browse for <hometheaterforum>. It comes top of the hits list on Google.

    Join and do a search on <pb10-isd) They are technically clued-up bunch and the SVS designers and directors post there regularly.

    Stacking is actually a damned good idea if you co-locate and calibrate properly. As you probably know you can turn the gain down on the stacked subs to compensate for the increased LF output. Usually about 6dB gain with two subs.

    Stacking increases headroom and lowers distortion. The multiple subs should behave as one much more powerful one sat in the same place in the room as a single one.

    Splitting subs up will usually confuse the issue in normal rooms. Since there must always be phase cancellation and reinforcement at some frequencies. Putting them very close together avoids this problem.

    Frank Manrique has 8 x 16-46 SV Subs co-located in his big HT system. The same idea as stacking boxes. But with cylinders stacked side by side instead of vertically.

    In theory there is probably no limit to how many subs you can stack as long as you can still see your screen across the room and the pile is completely stable. It's all about moving air. As you can see at any live rock concert. :)

    Regards
    Nimby
     

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  5. Magnet & Steel

    Magnet & Steel
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    what about rubber car mats to put between them? easy to cut, vibration free and pretty cheap.

    thats my 2 pence worth :)
     
  6. theo cupier

    theo cupier
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    Gnnn - I think I just heard the walls of my house crying at the thought of that!

    Having once made the mistake of standing at the front of a Motorhead gig, I recognise speaker walls like that! My hearing recovered 4 days afterwards (not even Metallica and Judas Priest inflicted that kind of damage)

    Presumably multiple numbers of the same sub will not produce any lower frequencies than the basic capabilities of the sub?

    Might there be some reduction in drop off at the bottom end - experienced if not measured (?) due to the lower distortion etc?
     
  7. bob1

    bob1
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    I doubt that ,once you have damaged the cell hairs in your ears they don't grow back.
    Think of it like this ,the airs move like corn in a field in a breeze as the wind gets stonger the corn starts to bend over some of the corn snaps off at the bottom some just bends over but does come back up , the more windy days (very loud noise) the more of the corn is damaged ,until one day all of the corn as gone.
    "what was that mate, speak up"
    Can you tell i've just been on a health&saftey course. :laugh:
     
  8. theo cupier

    theo cupier
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    Bob: PARDON?

    I'll see your H&S course and raise you a Life Sciences degree (really should know better, shouldn't I)

    I say recovered, what I probably mean is that my brain got accustomed to the constant tinnitus and dulled sound.
     
  9. Nimby

    Nimby
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    This is an interesting point much argued over on the other forum. Logic suggests that if the loudness of the the entire bass band lifts then lower frequencies ought to be reached. Simply because that part of the frequency fresponse is lifted too. But this does not occur in practice.

    Remember that all the individual subwoofers must each be reduced in gain to produce an overall match with the main speakers when all are playing bass test tones. The entire group of stacked subwoofers are calibrated overall just like any other speaker/ single subwoofer system. Or the deep bass would be too loud and overpowering just like a single badly-calibrated subwoofer.

    While dynamic transients may indeed achieve much higher SPLs, the individual subwoofers cannot produce a sound at a frequency below which they aren't individually capable of.

    So the roll-off point remains the same. But with a higher potential max SPL (dBs) at the roll-off point and above. Which must cause a steeper downward slope below the roll-off point. Or the frequency response would be extended downwards.

    I wish you hadn't asked this. :D Because I might have to got back and do my homework to double check if anyone questions the theory. :blush:

    Or perhaps they should just do their own homwork? :p

    Where's Frank M when you need him? :devil:

    Nimby
     
  10. Ian J

    Ian J
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    He posts here as El Cid and I believe that he now has a pair of the big brutes - B12/Plus4.
     
  11. eviljohn2

    eviljohn2
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    Car mat is also a good idea thanks, maybe even some foam between 2 bits of car mat. That way there's some isolation and no chance of either sliding away.

    WRT to getting more extension, this isn't the main aim of the activity but I think I may well be able to get a slightly lower extension out of the pair. The BK doesn't have a steep infrasonic filter at all (not as necessary in a sealed box as the air pressure acts as a spring to prevent the driver bottoming out). Those that have read the Budget Sub Test thread and review of the PB10 at the Secrets... website will know that the SVS PB10 and Mordaunt Short models have a very steep infrasonic filter which prevents them recreating very deep notes. With a pair of BK's I can reduce the overall gain on each due to the aforementioned 6dB increase (potentially more in a corner location :eek: ). By turning them both up a bit from there and reducing the higher bass notes with clever use of the BFD I think I'll be able to coax a bit more depth out of the pair than a single one would be able to provide at a sensible volume level, essentially due to the additional headroom that I'll have available.

    Time will tell if this works or just results in a horribly flat equalised sound. :)
     
  12. shodan

    shodan
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    I have a Velodyne Deco sub stacked on top of another sub (DIY jobbie), seperated by Mo-Pads.
    I've tried seperate locations for them but it was nothing but grief! And very muddled/poor quality bass. I now (after using a BFD) have much better "quality" of bass although I have to say theat I don't think its louder and I've not turned down the gain at all. But this may be as its no longer exciting the room nodes and the output has been tuned by the BFD settings....
     
  13. eviljohn2

    eviljohn2
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  14. GFS AV

    GFS AV
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    Any chance of a more in depth review?
     
  15. eviljohn2

    eviljohn2
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    Not for a couple of weeks I'm afraid. I'm slap bang in the middle of some exams at the moment (18% of my degree this week :eek: ). I've made sure it works and put it in location but that's about it.

    Hopefully in a few weeks I'll have a computer with a fast enough processor to actually run TrueRTA so I should be able to set them up with my BFD reasonably quickly and accurately.

    I'm planning to run them both from the LFE output of my Marantz SR7400 amp so they'll be receiving an identical signal, otherwise that's about the best I can do I'm afraid. :)
     
  16. GFS AV

    GFS AV
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    evil john,

    bet you wish it was a degree in AV equipment :)

    or is it? :laugh:
     
  17. eviljohn2

    eviljohn2
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    Not far off mate, it's a degree in Physics so covers more of the AV theory than equipment itself. :laugh:

    I would like to try and pursue a career in the AV industry but that's a different matter and isn't the easiest career ladder to jump onto unfortunately. :)
     
  18. Ed Selley

    Ed Selley
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    Of course with a degree in war and a fear of electricity I was a natural for it :clown:.
     
  19. eviljohn2

    eviljohn2
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    Hi guys

    I've had the pair for a week or so now and wanted to give a quick report on the performance. Also anyone can chime in with where I'm going wrong as there are plenty of details that I'm not sure about.

    First off, 2 BK's looks stunning. It's a beaming monster in the corner with 2 10" drivers showing but there's pic earlier on in the thread for that.

    I've got my equipment setup as follows: Front speakers set to large, crossover at 100Hz, bass mix to both. This is how the system sounds best to me for music and is therefore how it will stay. Full details of my equipment are in my article (link in sig).

    After spending a while playing with the phase controls (because it was fun to remove practically the entire sub-bass output with the turning of one dial) I got onto setting it up a bit further. All of my channel levels were calibrated using my RS Analogue Meter (the new model 33-4050). The subs are connected to the LFE output from my amp by a splitter. I set the amplifiers sub channel volume to +3dB and then calibrated each sub in turn (with the other switched off) as I would normally. Then I turned them both on and adjusted the amps channel volume so that the total output was correct (this turned out to be -1dB on the amp so there was a 4dB difference between the pair).

    As far as listening tests go, I havn't had much chance to play but the most obvious difference is the huge amount more power that's available. When people talk about "effortless" bass I now know what they mean. There's just so much more headroom available which is obvious during a few scenes in X2 and LOTR:TT:EE. I say obvious because the output actually seemed less implying that there's a fair bit less distortion going on.

    There's not a huge amount of difference with music, the biggest problem is that the bass suddenly becomes very directional as I can feel it through the floor in time to the music! I'll have to think about a good way of isolating them properly.

    I've been wrestling with TrueRTA and my SPL meter to try and get some useful readings out, but my computer is hideously under spec for it and the RS meter is a confusing beast at the best of times when it comes to proper calibration.

    I've attached a plot to give people an idea of the results I'm getting so far which seem too good to be true although I do know that my room exhibits a substantial peak at ~100Hz. These were gained by using 10 seconds of pink noise at 1/24 Octave resolution although I've smoothed the graphs down to 1/6 Octave. I also used the correction values given on the SVS site for the old RS meter, I've heard that the phono output of the meter might not be subject to correction although I find this hard to believe, can anyone advise on the right course of action?

    Before starting I checked my soundcard by patching a lead from the line out to the mic in and performing the same pink noise test. I decided that the soundcard (Awe64 value) was as flat as any is likely to be so am ignoring it.

    The green line represents my sytem as described earlier with subs being used. The purple line represents source direct so there is now subwoofer output. Also bear in mind that the actual dB values are completely irrelevant as I havn't calibrated the voltage readings. :)

    Edit: SPL meter was set to C weighting and fast speed. If anyone can tell me where to get a cheap calibration microphone then I'd be a happy person.
     

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  20. Diamond

    Diamond
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    Hmm, interesting.. Care to share a bit more about this 'mystic' filter?

    What do you classify as a deep note? Most of all are happy with :devil: 15-18 Hz, -3db or flat. :thumbsup:
     
  21. eviljohn2

    eviljohn2
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    I don't think there's anything mystic about them. :laugh:

    In order to protect the driver and amp from overloading, most subs have a low-cut infrasonic filter to keep out the "very deep" bass notes. We found in the Budget Sub Test (there's a link in my sig) that the Mordaunt Short 309 and 909 had a steep rolloff below about 23Hz which seemed to prevent the 909 exercising it's size advantages over the 309. Ed Mullen comments on the PB10's infrasonic filter in the paragraph just above the first response plot (the ground plane test). :)
     
  22. lowrider

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    Please explain speakers large, xover 100hz, what goes to the subs ?

    I have two Strata IIIs connected to LFE, xover 100hz, but all speakers small and subwoofers behind each front speaker, very flat response, to the ears, measurements show a bit of a boost before 50hz, but it sounds nice, like a bit of the old loudness, and no directional bass here...
     
  23. eviljohn2

    eviljohn2
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    The bass mix is set to "Both" so the LFE signal is sent to the subs and to my main speakers. My main speakers are only small bookshelves (Mission 771e) so I don't have any integration problems at low frequencies.

    The bass itself isn't really the problem when it comes to directionality, more that it's very noticeable that the floor shakes in time to the music. Wearing shoes pretty much solves this! I'm only using doorstops as feet though which is more functional than anything else. :)
     
  24. lowrider

    lowrider
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    Hmmm... I would not set them as large, less dynamic range, more distortion, more difficult integration, unless bass management is poor in your receiver... :confused:
     
  25. eviljohn2

    eviljohn2
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    I don't understand. :confused:

    You say that you would not set them to small, and I havn't set them to small. They're set to large. :)
     
  26. lowrider

    lowrider
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    Oops... I mean large, of course... :blush:
     
  27. eviljohn2

    eviljohn2
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    That's what I thought ;)

    I've been through all of the bass management combinations available (quite a few on my Marantz 7400) but eventually settled on my current configuration. Having them all set to small just seems lifeless although it worked much better with my old Denon 1802.

    There aren't any issues with the amplifier driving the speakers, the 7400 has buckets of power available and the 771e's dont drop below 6ohms across the frequency range. I think when I get some larger speakers I'll be using the small setting instead if that helps. :)
     
  28. lowrider

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    What you probably get with those settings is "doubling" the bass between 100hz and whatever your speakers go down to, kind of loudness...

    A friend used high level input plus low level input on his REL with the same effect, until I showed him what it really does, you may be better of increasing the volume on the subwoofers, then again, it might excite a room node and sound boomy, whatever sounds better for you... :rolleyes:
     
  29. Nimby

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    Why set your SPL meter set to "Fast"? :confused:

    Whatever your misgivings about the Radioshack meter it does the job well enough provided you add in the correction factors in the bass. (i.e. don't blame the messenger! :p

    I'm wondering about that 15Hz hump. Not much sign of steep infrasonic filtering there. :devil:

    I'm interested why you consider your computer is a problem using RTA and pink noise. RTA is a known CPU time guzzler.

    Would spaced, single-frequency test tones (using "C-slow" ) and Excel have produced markedly different results? :confused:

    Nimby
     
  30. eviljohn2

    eviljohn2
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    Nimby,
    SPL meter is set to fast as I'm not after an averaged output here. I can do that using the RTA program if necessary. It shouldn't make much difference as I'm only measuring noise but I can do a comparison between fast and slow if you like.
    The RS SPL meter seems to be working OK for it but I'm sure a proper calibration mic would do a better job as it doesn't include the weighting networks.
    As far as computer speed goes, I'm using a Pentium 133 for this. Minimum spec for TrueRTA claims 500MHz Pentium3 but it seems to be working as long as I'm very careful not to run it too long, save frequently and put up with it crashing every 15 minutes or so. :rolleyes:
    Using regularly spaced test tones would have been more akin to using white noise which isn't the ideal here. Plus it would have taken ages to get 1/24 resolution rather than the few seconds each plot takes using the software.

    Diamond,
    The BK uses an "off the shelf" DIY amp panel so I don't think it will incorporate a substantial infrasonic filter as the panel wasn't designed specifically around this design. Perhaps Dan Gleebles can clarify if the BK panel has any onboard filters/EQ?

    Lowrider,
    Following your suggestions I've been tweaking and think I'm definitely getting somewhere now with the speakers set to small. Thanks. :thumbsup:

    Attached is my latest set following an afternoon tweaking. The blue line is with the subs being used and speakers set to small. The orange line is "Source Direct" which sets the speakers to large and doesn't use the subs at all. I've set the subs crossovers to ~80Hz and both of the gain controls are on ~1/3 of maximum.

    These results are very impressive so I think I'll stick here with the settings. When I get my BFD online (ie. when CPC deem to send me the 1/4" connectors I've been waiting a month for) then I can deal with the peaks in the high 20Hz and high 90Hz regions. Having been doing this all afternoon I'm satisfied that these results are as genuine as I can get them, they're shown here in all of the 1/24 octave resolution glory. I don't think the dual BK combination is one to be sniffed at in any respect, it's starting to sound absolutely phenomenal and shift more air than anything else I've heard. :)
     

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